Systems and methods of thermal energy storage and release

ABSTRACT

Thermal energy storage systems and devices comprise at least one storage vessel, at least one heat transfer ramp adjacent to the at least one storage vessel, and at least one heat transfer fluid channel adjacent to the heat transfer ramp. Heat exchange occurs between a heat transfer medium traveling down the heat transfer ramp and a heat transfer fluid traveling through the heat transfer channel. The heat transfer ramp may be angled with respect to the storage vessel such that the heat transfer medium travels down the heat transfer ramp assisted by force of gravity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 12/881,102, filed Sep. 13, 2010, which is hereby incorporated by reference in its entirety, which claims priority to U.S. Provisional Patent Application Ser. No. 61/241,909, filed Sep. 13, 2009, which is incorporated by reference herein in its entirety.

FIELD

The present disclosure is in the technical field of Thermal Energy Storage (TES).

BACKGROUND

In concentrated solar power (CSP) or similar energy systems, heat transfer fluid (HTF) is used to convey energy from the heat source to and/or from the energy conversion or use system. In CSP systems, the heat source is an array of concentrating solar collectors, and the energy conversion system is typically a heat engine such as a steam cycle or organic Rankine cycle. In CSP systems in particular, the functionality and, potentially, the economic worth of the system is enhanced by thermal energy storage (TES). The benefit of TES comes from extending the operating time of the energy conversion system or shifting the time of energy production to a more favorable time when energy is more valuable.

Various TES technologies have been developed, particularly for CSP applications, including the two-tank TES system and the single-tank thermocline, both of which have direct and indirect variations (referring to whether the HTF and thermal storage medium are the same or are segregated and interfaced through a heat exchanger). Each of these technologies has pros and cons related to system cost effectiveness, commercial history, and operational attributes. For example, a two-tank system using HTF with high vapor pressure requires plants at high temperature HTFs requires costly pressurized storage tanks. Systems with molten salt varieties as a HTF and/or thermal storage media require specialized tanks and heat exchanger designs. The single-tank thermocline can be a cheaper option due to reduced capital costs, yet must consider the same issues with the type of HTF used. In general, current TES technologies require heat transfer fluids and thermal storage mediums with significant cost and design implications.

The use of granular material such as sand would expand currently available thermal energy storage medium options. However, because sand is an abrasive solid, this requires new technical solutions to effectively utilize the material. Thus, there is a need for thermal energy storage systems and methods that can effectively use inexpensive granular materials as a storage medium and are compatible with a variety of heat transfer fluids.

SUMMARY

Embodiments of the present disclosure provide alternatives to, and alleviate many of the disadvantages of TES systems by providing thermal energy storage devices, systems and methods which utilize granular materials as a thermal energy storage medium that is compatible with a variety of HTFs. Disclosed systems include combined heat exchange and conveyance systems in which thin layers of granular heat transfer material are cascaded down a network of ramps adjoined to heat transfer fluid channels such that heat transfer occurs between the heat transfer material and the heat transfer fluid. This thin flow is particularly advantageous because it boosts heat transfer effects by increasing the surface area of the heat transfer medium contacting the heat transfer fluid.

At least one heat transfer ramp is adjacent to at least one heat transfer fluid channel, and the heat transfer ramp is angled such that a granular material travels down assisted by force of gravity so heat exchange occurs between the granular material and a flow of heat transfer fluid traveling through the heat transfer fluid channels. Any number of ramps can be stacked in parallel or in a zig-zag configuration with heat transfer fluid channels in between the ramps or linked to the sides of the ramps to optimize heat transfer. Embodiments of the present disclosure effectively use sand, a relatively inexpensive and environmentally benign material, as a thermal storage medium while also providing heat transfer and heat exchange capabilities. Alternative granular materials would include any particles capable of acceptably handling the temperature parameters in a given application, whether it be a heating or cooling application.

Other advantages of the disclosed systems and methods include, but are not limited to: (1) use of sand or other inexpensive and inert granular material as the storage medium, which is environmentally benign, inexpensive, non-volatile, acceptable in thermal properties, (2) delivery of a constant temperature heat from the silos since a relatively constant temperature will be maintained in the bins irrespective of current sand volume, (3) compatibility with a variety of HTF fluids, as the design is adaptable to various HTFs and TES media, (4) achievement of high “round trip thermal efficiency” since energy loss is minimal, and (5) applicability to other CSP technology and other thermal systems.

Exemplary embodiments of a system of thermal energy storage and release comprise at least one storage vessel, at least one heat transfer ramp adjacent to the at least one storage vessel, and at least one heat transfer fluid channel adjacent to the heat transfer ramp such that heat exchange occurs between a heat transfer medium traveling down the heat transfer ramp and a heat transfer fluid traveling through the heat transfer channel. The heat transfer ramp is angled with respect to the storage vessel such that the heat transfer medium travels down the heat transfer ramp assisted by force of gravity. In exemplary embodiments, the heat transfer medium is a granular material. In exemplary embodiments, the storage vessel may be insulated to govern its contents' heat exchange with the surrounding environment.

In exemplary embodiments, the system may further comprise a distribution mechanism operatively connected to the heat transfer ramp to evenly spread the granular material. The at least one ramp could comprise at least two ramps in a substantially parallel layered configuration or at least two ramps in a cascading configuration. The at least one heat transfer fluid channel may be disposed between the two ramps. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, or a bottom surface of the heat transfer ramp. In exemplary embodiments, the at least one ramp defines a textured or channeled surface or defines at least one slot. The ramp could also vibrate to assist flow of the heat transfer medium.

The at least one heat transfer fluid channel may comprise a system of tubes or parallel plates linked to the ramps. In exemplary embodiments, the system further comprises at least one height adjustment mechanism operatively connected to at least one of the at least one ramp(s) to change the flow direction of and/or regulate the rate of flow of the heat transfer medium. The at least one storage vessel may comprise a first and second storage vessel and the at least one ramp comprises a first ramp removing the granular heat transfer medium from the first storage vessel and a second ramp delivering the heat transfer medium to the second storage vessel. In exemplary embodiments, energy is stored as heat gathered by, or discharged to, a concentrating solar thermal power plant.

Exemplary embodiments include methods of storing thermal energy comprising providing a granular material and a heat transfer fluid. The methods include conveying the granular material through at least one ramp angled with respect to a storage vessel such that granular material travels down the heat transfer ramp assisted by force of gravity and conveying the heat transfer fluid through at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The granular material may travel in overall counterflow to a flow of heat transfer fluid, or flow could be generally concurrent or cross-current. In exemplary embodiments, the granular material is sand. Exemplary methods may further comprise evenly distributing the granular material in the ramp.

In exemplary embodiments, methods further comprise adjusting the height of at least one of the at least one ramp(s) to change the flow direction and/or speed of the granular material. Exemplary methods also include providing a first and second storage vessel, removing the granular material from the first storage vessel, and delivering the granular material to the second storage vessel. Exemplary methods may also include releasing stored thermal energy comprising providing a granular material and a heat transfer fluid. The granular material is conveyed through at least one ramp angled with respect to a storage vessel such that granular material travels down the heat transfer ramp assisted by force of gravity. The heat transfer fluid is conveyed through at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid.

Exemplary embodiments include a combined heat exchange and conveyance system comprising a bundled heat transfer assembly including at least two stacked heat transfer ramps and at least one heat transfer fluid channel adjacent to the at least two stacked heat transfer ramps. A heat transfer medium is conveyed through the heat transfer ramps such that the heat transfer medium travels down the heat transfer ramps assisted by force of gravity, and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs in the bundled heat transfer assembly between the heat transfer medium and the heat transfer fluid.

The heat transfer medium may be a granular material. The heat transfer medium travels in overall counterflow to a flow of heat transfer fluid or in overall co-current flow to a flow of heat transfer fluid. In exemplary embodiments, the heat transfer ramps define at least one slot such that the heat transfer medium falls through the at least one slot in a first heat transfer ramp to a second heat transfer ramp below the first heat transfer ramp. The system may further comprise at least one storage vessel, wherein the heat transfer ramps are angled with respect to the storage vessel. The at least one heat transfer fluid channel may be disposed between the two stacked heat transfer ramps. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, and/or a bottom surface of the heat transfer ramp.

In exemplary embodiments, a thermal heat transfer device is provided comprising a combined heat exchanger and conveyor including at least one heat transfer ramp and at least one heat transfer fluid channel adjacent to the heat transfer ramp. A granular material is conveyed through the at least one heat transfer ramp such that the granular material travels down the heat transfer ramp assisted by force of gravity, and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. In exemplary embodiments, the granular material is sand.

The heat transfer channel may be angled in relation to the at least one heat transfer ramp. In exemplary embodiments, the ramp comprises at least two ramps in a substantially parallel layered configuration, and the at least one heat transfer fluid channel may be disposed between the two ramps. The ramps may define at least one slot such that the heat transfer medium falls through the at least one slot in a first ramp to a second ramp below the first ramp. In exemplary embodiments, the ramp comprises at least two ramps in a cascading configuration. In exemplary embodiments, the at least one heat transfer channel is coupled to one or more of a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, and/or a bottom surface of the heat transfer ramp.

Exemplary embodiments include a heat exchanger that is comprised of an Archimedes screw conveyor design to transport sand over an internal HTF tube bundle, which contains heat transfer fluid used to store and remove heat from the sand. In exemplary embodiments a system of energy storage and release comprises at least one storage vessel and a combined conveyor and heat transfer device linked to the at least one storage vessel by at least one discharge device. The combined conveyor and heat transfer device includes a rotatable conveyor drum and at least one heat transfer fluid channel within the rotatable conveyor drum. A granular material travels from the at least one storage vessel to the combined conveyor and heat transfer device via the at least one discharge device. The rotatable conveyor drum moves the granular material therethrough in counterflow to a flow of heat transfer fluid traveling through the heat transfer fluid channel. In exemplary embodiments the granular material is sand.

In exemplary embodiments, the rotatable conveyor drum may be an Archimedes screw and may comprise one or more vanes fixed to an inner surface of the drum. The one or more vanes may be spiral shaped, longitudinally straight, substantially T-shaped or substantially V-shaped in cross-section to distribute the granular material over the heat transfer fluid channels. The at least one heat transfer fluid channel may comprise a plurality of tubes arranged in a bundle. In exemplary embodiments, when the rotatable conveyor drum rotates the granular material pours over the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The one or more vanes may pick up and rain the granular material over the at least one heat transfer fluid channel.

In exemplary embodiments, the at least one storage vessel comprises a first and second storage vessel, and the first storage vessel has a higher temperature than the second storage vessel. The at least one storage vessel may be located above or below ground level and may have at least one angled wall. In exemplary embodiments, the stored energy is heat gathered by, or discharged to, a concentrating solar thermal power plant.

Exemplary embodiments include methods of storing thermal energy. Exemplary methods comprise providing a granular material and a heat transfer fluid. The heat transfer fluid has a temperature relatively higher than a temperature of the granular material. The granular material and the heat transfer fluid are conveyed such that the granular material continually pours over a tube carrying the heat transfer fluid such that heat exchange occurs between the granular material and the heat transfer fluid. A set of vanes may direct the pouring of the conveyed granular material, and the granular material may be sand. The granular material may travel in overall counterflow to a flow of heat transfer fluid or in overall cocurrent flow to the flow of heat transfer fluid.

Exemplary methods may further include methods of releasing stored thermal energy comprising providing a granular material and a heat transfer fluid. The granular material has a temperature relatively higher than a temperature of the heat transfer fluid. The granular material and the heat transfer fluid are conveyed such that the granular material pours over a tube carrying the heat transfer fluid such that heat exchange occurs between the granular material and the heat transfer fluid. The result of this exchange is that the granular material is cooled and the HTF is heated.

In exemplary embodiments, a combined conveyor and heat transfer device comprises a rotatable conveyor drum and at least one heat transfer fluid channel within the rotatable conveyor drum. The rotatable conveyor drum moves a granular material therethrough in counterflow to a flow of heat transfer fluid traveling through the heat transfer fluid channel. The rotatable conveyor drum may be an Archimedes screw. When the rotatable conveyor drum rotates, the granular material pours over the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid. The rotatable conveyor drum may be capable of rotating at one or more speeds.

Accordingly, it is seen that thermal energy storage devices, systems and methods are provided which effectively use granular materials as a thermal storage media while also providing heat transfer and heat exchange capabilities. These and other features and advantages will be appreciated from review of the following detailed description, along with the accompanying figures in which like reference numbers refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of the present disclosure, showing a thermal energy storage and release system with above ground storage vessels containing sand thermal storage medium;

FIG. 2 is a front view of an embodiment of a rotatable conveyor drum containing the heat transfer tube bundle in accordance with the present disclosure;

FIG. 3A is a side view of an embodiment of a rotatable conveyor drum containing an embodiment of a heat transfer tube bundle in accordance with the present disclosure;

FIG. 3B is a side view of an embodiment of a rotatable conveyor drum containing an embodiment of a heat transfer tube bundle in accordance with the present disclosure;

FIG. 4 is a top view of an embodiment of a supply and return piping arrangement for a heat transfer tube bundle in accordance with the present disclosure;

FIG. 5 is a perspective view of an embodiment of a thermal energy storage and release system with in-ground storage vessels containing sand thermal storage medium in accordance with the present disclosure;

FIG. 6 is a side view of an embodiment of a thermal energy storage and release system with in-ground storage vessels during the thermal energy storage charging process in accordance with the present disclosure;

FIG. 7 is a side view of an embodiment of a thermal energy storage and release system with in-ground storage vessels during the thermal energy discharge process in accordance with the present disclosure;

FIG. 8 is a side view of an embodiment of a storage vessel of a thermal energy storage and release system in accordance with the present disclosure;

FIG. 9 is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 10A is a side view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 10B is a side view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 10C is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 11A is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channels in accordance with the present disclosure;

FIG. 11B is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channels in accordance with the present disclosure;

FIG. 11C is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channels in accordance with the present disclosure;

FIG. 11D is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channel in accordance with the present disclosure;

FIG. 11E is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channel in accordance with the present disclosure;

FIG. 11F is a cross-sectional view of an embodiment of a heat transfer ramp and heat transfer channel in accordance with the present disclosure;

FIG. 12A is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 12B is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 12C is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 13A is a side view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 13B is a perspective view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 14 is a side view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 15 is a perspective view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 16A is a perspective view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 16B is a side view of an embodiment of an energy storage and release system in accordance with the present disclosure;

FIG. 17A is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 17B is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 17C is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 17D is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 17E is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 17F is a top view of an embodiment of a heat transfer ramp in accordance with the present disclosure;

FIG. 18A is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 18B is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 19 is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 20 is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure;

FIG. 21 is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure; and

FIG. 22 is a cutaway view of view of an embodiment of a combined heat exchanger and conveyor in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

In the following paragraphs, embodiments will be described in detail by way of example with reference to the accompanying drawings, which are not drawn to scale, and the illustrated components are not necessarily drawn proportionately to one another. Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than as limitations of the present disclosure. As used herein, the “present disclosure” refers to any one of the embodiments described herein, and any equivalents. Furthermore, reference to various aspects of the disclosure throughout this document does not mean that all claimed embodiments or methods must include the referenced aspects.

With reference to FIGS. 9-22, exemplary embodiments of systems of storing and releasing thermal energy utilizing gravity assisted flow of heat storage materials will now be described. Embodiments of disclosed systems are sometimes referred to as a “Ramp SandShifter” or “Column SandShifter.” An exemplary Column SandShifter is shown in FIG. 15 and may also include one or more ramps. A schematic overview of an exemplary thermal energy storage and release system 110, or Ramp SandShifter, can be seen in FIGS. 10A-B. The system 110 includes one or more storage vessels 112 a, 112 b, at least one of which contains a heat transfer medium 115, which could be a granular material that functions as a thermal energy storage medium. The heat transfer medium 115 could be sand or any other organic or inorganic materials in granular form that can store energy in the form of heat or might be warm and provide a benefit from being cooled. Exemplary granular materials include sand such as silica sand or barytes sand (barium sulfate), partially calcined clay, glass beads, and reclaimed petroleum catalysts. The storage vessels 112 could be situated above or below ground, and there could be a plurality of storage vessels used as part of the system.

The system 110 further comprises a combined heat exchanger and conveyor 111, which includes one or more heat transfer ramps 114 located adjacent to the storage vessels 112, or linked thereto, and extending into each storage vessel 112. The ramps 114 may be mechanically linked to the storage vessels 112 either indirectly through attachment to one or more vertical conveyors 116 connecting a pair of storage vessels 112 or directly through attachment of a first end 118 of the ramp 114 to the interior bottom 120 of a storage vessel 112. Supporting structures 119 of various sizes may be provided to support the ramp 114 and achieve the desired angle of the ramp 114. Additional linkages could be provided as well, and it should be understood that any linking of the ramps 114 to the storage vessels 112 could be used so long as the granular material 115 can pass freely between the ramps and the storage vessels.

As best seen in FIGS. 12A-C, the combined heat exchanger and conveyor 111 further includes one or more heat transfer fluid channels 122 in close enough relation to the ramps 114 to allow heat transfer between the granular material 115 acting as a thermal energy storage medium and a heat transfer fluid (HTF) 128. More specifically, heat is exchanged between the shared walls of the heat transfer ramps 114 and the heat transfer fluid channels 122 so the heat transfer medium 115 is effectively heated or cooled. Any known HTF could be used, including oil, water, steam, molten salt, synthetic HTFs such as Therminol VP-1, or any other fluid or gas with which heat exchange occurs. Many configurations of heat transfer ramps and channels can be utilized so long as the granular material and HTF are sufficiently close to permit effective heat transfer. Multiple heat transfer ramps 114 could be arranged in a substantially parallel layered, or stacked, configuration. As discussed in more detail below, the layered configuration could comprise two or more ramps 114 in a straight stack directly on top of each other so the sides are flush, or could be in a parallel cascading or zig-zag arrangement.

In some embodiments, the heat transfer channels 122 are adjacent the ramps 114 or in direct contact with the ramps 114. The heat transfer channels 122 could be enclosed tubes, open plates or ramps, or spaces created in between the ramps 114 when the ramps are in a stacked configuration. For high pressure HTF applications (e.g., steam) the heat transfer channel 122 would likely be in the form of an enclosed pipe. For lower pressure HTF applications, the heat transfer channel 122 would likely be open, such as a thin, flat channel, perhaps located parallel to the ramps 114. While rounded pipes handle higher pressures better since there are no uneven pressures that create deformities, either form of channel could be used in either circumstance. As shown in FIGS. 11B and 12A, the channels 122 can be coupled to the bottom surface 121 of each ramp 114 at any location along the bottom of the ramp. Alternately, or in addition to bottom coupling, the channels 122 could be coupled to one or more of the side surfaces 123 of the ramp 114, as shown in FIGS. 11A and 12B.

As illustrated in FIG. 12C, instead of running parallel to the heat transfer ramp, the heat transfer channel 122 could be configured at an angle relative the heat transfer ramp 114 so that HTF 128 flows longitudinally up or down at an oblique angle relative to the latitudinal flow of heat transfer medium 115. In some embodiments, as shown in FIG. 11F, channels 122 could be coupled to a top surface 125 of the ramp 114. In some embodiments, as illustrated in FIGS. 11C-D, the ramp 114 may be hollow and define one or more tubes or passages 130 within it through which the HTF 128 flows. Alternately, the ramps 114 and heat transfer channels 122 may be arranged side by side with the heat transfer channels being flat ramps similar in structure to the heat transfer ramps 114.

In exemplary embodiments, multiple heat transfer ramps 114 are joined together in various configurations to form a network of ramps and heat transfer channels 122. Turning to FIGS. 9, 12A-B and 14, one example is a parallel layered configuration in which at least two heat transfer ramps 114 are stacked on top of each other. FIGS. 18A-B show a cutaway view of a straight parallel layered configuration. Such a system of stacked ramps 114 has, alternately, granular material 115 flowing through a ramp 114 with HTF 128 flowing through a channel 122 coupled to the bottom 121 or side 123 of the ramp 114, then granular material 115, then HTF 128, in succession through any number of ramps and channels. The granular energy storage material 115 flows down each ramp 114 while HTF 128 is either pumped upwards or flows downwards through the heat transfer channels 122, shown here as externally linked tubes 132. As shown in FIGS. 10-11, a system of ramps could be provided in which one or more heat transfer ramps 114 are aggregated into a collected assembly forming a bundle 108.

Two or more parallel heat transfer ramps 114 could also be linked in a cascading, or zig-zag, configuration. As shown in FIGS. 13A-B, the ramps 114 employed in this arrangement may be shorter plates to reduce the amount of space needed for the thermal energy storage and release system 110. FIGS. 19 and 20 show close up views of the angled ramps 114, with a smooth zig zag configuration in FIG. 20. The granular energy storage material 115 flows down the ramps or plates 114, zig-zagging from plate to plate while HTF 128 is pumped upwards through the heat transfer channels 122, shown here as internal tubes 130. A cascading configuration could allow for directional adjustment as the individual plates could “toggle” directionally relative to each other to allow for direction change of the granular material 115 and HTF 128 without moving the entire ramp system. Indeed, a wide range of different angles between cascading ramps could be employed depending on the application. FIG. 21 shows a network of cascading ramps 114 with a corrugated fin configuration.

As described in more detail herein, heat transfer from the energy storage medium to the HTF is achieved by gravity assisted flow of the granular material functioning as the storage medium down or along the surface of the ramps. To effectively utilize gravity to move the granular material, the ramps are deployed at various angles relative to the ground and relative to the storage vessels. The ramp angle could be anywhere from 0° to 90°, or perpendicular to the ground, i.e., vertically oriented. It should also be understood that the ramps could be fixed or could have a height adjustment mechanism 132 to elevate or lower the respective ends of the ramp and change the flow direction of the energy storage medium. Height adjustment mechanisms could be any known mechanical or electronic system including motors, etc. An example of a combined heat exchange and conveyance system 111 at a relatively steep angle is depicted in FIG. 10C.

Turning to FIGS. 17A-F, embodiments of the heat transfer ramp 114 could have different surface features. For instance, the surface 134 of the ramp 114 could define channels 136 therein for facilitating the flow of the granular material 115, and the channels 136 may have different patterns or features. Exemplary channels may be straight, curved or zig-zag. A textured surface is also possible having small protrusions 138 to create the texture. The ramp surface could, of course, be smooth and without channels. Another contemplated ramp feature that would aid in the flow of the granular material 115 is that the ramp could have the ability to vibrate, as shown in FIG. 14D. Such vibrations 117 could be achieved via a motor or electromechanical mechanisms. As shown in FIGS. 17E-F and 22, the heat transfer ramps 114 may define one or more slots 127 or punctures. This feature is advantageous in parallel stacked and cascading configurations as it allows the heat transfer medium 115 to fall through the slots 127 from one ramp 114 to the next ramp 114 below. The slots and punctures may also offer heat transfer advantages due to the thermal storage media's contact with their enlarged and/or angled surface area as it passes through.

In operation, high temperature HTF 128 is pumped to the site of the energy storage and release system 110, having been heated, for example, by a renewable energy facility such as a concentrating solar thermal power plant 105. Meanwhile, vertical conveyor 116, best seen in FIG. 15, lifts and conveys a granular material 115 having a temperature cooler than that of the HTF 128 from a first storage vessel 112 a up to a top entry point of a heat transfer ramp 114. The granular material 115 is then loaded into the heat transfer ramp 114 and, assisted by the force of gravity, flows down the ramp toward a second storage vessel 112 b. In stacked parallel configurations, whether straight or cascading, the granular material 115 feeds from the end of one ramp 114 into the start of another ramp 114. In addition, the granular material 115 may flow from the sides 123 of one ramp 114 into a ramp below, as well as through the above-described slots 127 from ramp to ramp. The operator could optimize the loading process and initial descent of the granular material 115 by using a distribution mechanism 113 such as a fan, sieve, plenum, shaped outlet, or a system of channels to spread the granular material 115 in the desired manner, such as an even distribution, at the top of the ramp 114.

As discussed above, additional ramp features such as channels, a textured surface, or vibrations 117, could also aid the flow of the granular material 115. It should also be noted that the operator of the energy storage and release system 110 could change the orientation and angle of the heat transfer ramp 114 to optimize flow of the granular material 115. Any ramp angle, including a 90° vertical orientation could be employed. Significant advantages of the systems described, especially the various ramp structures, features, and layouts, are that the conveyed granular material 15, 115 is retarded so it moves in a soft flow, reducing abrasiveness, and as the conveyed granular material 15, 115 falls slowly in a thin layer, it provides increased time and surface area contact to improve heat transfer to or from the granular material.

In exemplary embodiments, the HTF 128 flows through one or more of the heat transfer channels 122 in counterflow, co-current flow, or cross-current flow to the granular material 115. As discussed above, the HTF 128 could flow through heat transfer channels 122 which are internal tubes 130 within the ramps 114 or externally linked tubes 132. In this way, the HTF 128 adsorbs or gives up heat, which is transferred to the granular material 15 functioning as a thermal energy storage medium. The granular material 115, now hot from the heat transfer, exits the heat transfer ramp 114 into the second storage vessel 112 b, where it is stored until the thermal energy is needed.

The thermal energy storage process would be similar when employed using other exemplary embodiments described above, such as parallel stacked or layered configuration of heat transfer ramps 114 or a cascading configuration of shorter ramps or plates. It may be advantageous for the granular material 115 to travel in cocurrent flow relative to the flow of HTF 128. In such embodiments, the HTF 128 may flow downward through the heat transfer channels 122 as the granular material 115 flows down the heat transfer ramps 114, as illustrated in FIG. 16. It also should be noted that the relative flow direction of the granular material 115 and the HTF 128 could be changeable so that it is neither cocurrent nor in counterflow, but some relative flow direction in between. Such cross-current flow could be implemented so the granular material 115 and HTF 128 flow in any direction relative to the other. As mentioned above, the system operator could “toggle” or adjust the direction of one or more of the cascading ramps 114 or plates to change the flow direction of the granular material 115 relative to that of the HTF 128.

To release the thermal energy stored in the storage medium, the hot granular material 115 is lifted by the vertical conveyor 116 from the second storage vessel 112 b up to a top entry point of a heat transfer ramp 114. The granular material 115 is then loaded into the heat transfer ramp 114 and flows down the ramp toward a second storage vessel 112 b, with the aid of gravity. At the same time, HTF 128 having a temperature cooler than that of the granular material 115 is distributed through heat transfer channels 122 and flows in counterflow to the hot granular material 115. Thus, the granular material 115 exchanges heat with the HTF 128 as they flow adjacent each other. The now cooler granular material 115 reaches the lower end point of the heat transfer ramp 114 and exits into storage vessel 112 a where it awaits another round of thermal energy storage. The now hot HTF 128 may be used to produce usable energy by known methods such as providing steam for a turbine. It should be noted that any of the variations discussed above could be employed in the energy release mode, including different relative flow directions of the granular material 115 and HTF 128, different ramp angles and configurations, and different heat transfer channel arrangements.

It also should be noted that thermal energy storage and release are not the only functions provided by disclosed systems and methods. Heat exchange could be conducted for non-energy storage purposes such as use of the heated granular material 115 or HTF 128 for industrial heat or cooling or to directly provide power in various energy generation applications.

Referring now to additional embodiments of the invention in more detail, FIG. 1 depicts an exemplary embodiment of a thermal energy storage system (sometimes referred to herein as a “Rotating Drum SandShifter”) that uses a very inexpensive and benign storage medium: sand or similar granular material. Exemplary embodiments of a sand-shifter thermal energy storage system consist of a higher temperature above ground vessel 2 as well as a lower temperature above-ground storage vessel 3, each filled with sand to function as the thermal energy storage medium. The lower temperature above ground storage vessel 3 contains only moderately warm sand that is available to be heated and store energy, and the higher temperature above ground storage vessel 2 contains hot sand after it has been heated to store energy.

As shown in FIGS. 1-3B, a system of energy storage and release 30 includes a combined conveyor and heat transfer device 40 comprising a conveyor 1, which may be an Archimedes screw conveyor and heat transfer fluid inner heat transfer tube bundle 8. In exemplary embodiments, the sand or similar granular material is moved by the conveyor in a direction 35 roughly in counterflow to the flow 38 of the heat transfer fluid 28, but cocurrent flow may also be employed. The HTF 28 will be circulated through a heat transfer tube bundle to contact the sand within the conveyor 1. The heat transfer tube bundle 8 may be one of various designs including a tube bundle of pipes, bare tubes, finned tubes, and/or plate heat exchangers; where the design consists of the basic concept of effectively transporting heat transfer fluid through the conveyor 1 to come into contact with the sand thermal energy storage medium. FIG. 1 provides an illustration of how the HTF heat transfer tube bundle 8 may be configured within the conveyor 1, which will pour sand or similar granular material 15 over the HTF 28 to adsorb or give up heat depending on whether the sand is being heated or cooled. Sand or other granular material enters the conveyor 1 via the horizontal discharge augers (or other suitable conveyor) 9, 10, and sand is recovered to the top of the storage vessels via vertical conveyors 6, 7.

It is understood that alternatively the granular material might be moved between the top and the bottom of a single vessel. It is also understood that the heat transfer tube bundle may employ finned tubes to promote heat transfer and distribution of the sand.

As shown in FIG. 1, when energy is being stored the lower temperature sand is removed from the lower temperature above ground storage vessel 3, heated by the heat transfer tube bundle 8 containing higher temperature HTF 28 from the solar collector field 4, 5 and transferred to the higher temperature above ground storage vessel 2. When energy storage is complete, the higher temperature above ground storage vessel 2 will be largely full of hot sand. When stored energy is needed, hot sand will be returned to the lower temperature above ground storage vessel 3 while stored heat in the sand is recovered by warm outlet HTF. The practical design shown allows free expansion and contraction of the metal parts to account for thermal expansion.

An exemplary conveyor used to move the sand is a variation of an Archimedes screw. The Archimedes screw is normally used as a type of lift pump. In this case, it is used as a sand conveyor and heat exchanger. As more specifically shown in FIGS. 2 and 3A-3B, the Archimedes screw conveyor 1 is a rotating sand conveyor drum 11 with one or more spiral vanes 12 fixed to the inner surface of the drum. As the drum turns, the spiral vane 12 pushes the sand 15 along the bottom of the rotating drum 11. The Archimedes screw has no close sliding fits to achieve this pushing motion; indeed, there is no sliding metal-to-metal contact at all. As the sand 15 is conveyed by the spiral vane 12, a set of longitudinal straight vanes 13 acts to simultaneously lift and convey the sand 15 over the heat transfer tube bundle 8 containing the heat transfer fluid (HTF) 28. By this action the HTF 28 flowing in the tubes 8 is made to either adsorb or give up heat. As shown in FIG. 1, vertical conveyors 6, 7 will top-load each storage vessel, and horizontal discharge augers or other conveyors 9, 10 will unload them from below.

The Archimedes screw sand conveyor 1 has the great advantage that switching the direction of rotation changes the direction of the motion of the sand. This feature makes it is easy to change the direction of the motion of the sand as the system is switched between the heat storage function and the heat recovery function.

Details of the Archimedes screw conveyor 1 are shown in FIGS. 2 and 3. The spiral vane 12 (the “screw” of the Archimedes screw) is shown attached to the interior of a drum 11. Inside the drum 11, is shown a heat transfer tube bundle 8 containing the HTF 28. As the drum 11 rotates, sand or other granular material 15 is pushed along laterally by the screw spiral vane 12. An advantageous feature is that the drum also carries a series of longitudinal vanes 13 that pick up and rain the sand 15 over the tube bundle, thus providing heat exchange as the sand 15 is conveyed (FIG. 3). Note again that the Archimedes screw has no close sliding fits and no sliding metal to metal contact at all, which is in contrast to an auger or screw conveyor. As the HTF 28 passes through the heat transfer tube bundle 8, the sand 15 pours over the pipes, either charging the HTF 28 with heat from hot sand or, conversely, charging the sand 15 with heat from the hot HTF 28. The tubes may be equipped with longitudinal or transverse fins to increase the outside heat-transfer area and to retard and redirect the fall of the conveyed sand 15 providing adequate time for heat transfer to or from the sand. In this application, the function of the tubes and fins is analogous to the action of the so-called “fill” in a cooling tower or packed column. The rotating drum 11 will be insulated 14 to avoid heat losses.

Various types of extended surfaces such as longitudinal, latitudinal, and/or corrugated fins may be used to increase the heat transfer surface on the sand side. Furthermore, the fins may have additional features to improve the contact between the flowing sand and the base tubes. In addition the tubes may have elongated or elliptical shapes to improve the contact and heat transfer with the sand. Indeed, the preferred “tube” cross section may be more plate like or similar to an elongated rectangular passage than a generally circular “tube”. These additional features enhance the contact between tube and fins with the sand and heat transfer to or from the sand may be included.

Various additional features to enhance heat transfer to or from the sand or from the tube to the internal heat transfer fluid may be included. In some situations, for example, it may be advantageous for the granular material to travel in overall cocurrent flow to the flow of internal heat transfer fluid. FIG. 3B illustrates an exemplary embodiment in which the sand or similar granular material 15 is moved by the conveyor in a direction 35 roughly in cocurrent flow to the flow 38 of the heat transfer fluid 28.

An overhead view of the supply and return piping, including the heat transfer tube bundle 8 is shown in FIG. 4. The heat transfer tube bundle 8 is integrated into the plant via inlet and outlet large central large diameter pipes 16, 17. These pipes are connected to the heat transfer tube bundle 8 through left and right hand large diameter pipes 18, 19, which are in turn connected to left and right hand plenums 20, 21. The plenums 20, 21 handle the transfer of HTF 28 between the large diameter pipes and the heat transfer tube bundle 8. It should be noted that the structural outriggers support the heat transfer tube bundle and both plenums at each end. This allows free expansion from the central support to account for thermal expansion.

It may be further understood that the option exists for the sand-shifter system to employ in ground storage vessels or pits as the storage volume as opposed to above ground storage vessels. FIG. 5 shows a perspective view of the sand-shifter thermal energy storage system with an in ground storage vessel setup. The main difference in this system is the need for vertical conveyors 24, 25 to transport sand out of the higher temperature in ground storage vessel 22 and lower temperature in ground storage vessel 23.

Embodiments of charging processes to store thermal energy in the sand are shown by a side view in FIG. 6. This process will be largely similar regardless if practiced with in ground or above ground storage vessels. Higher temperature heat transfer fluid inlet from the solar collector field 5 flows into the sand-shifter system by way of an inlet large diameter supply pipe 16. Next the hot HTF 28 flows through the left hand large diameter pipe (LHLDP) 18 into the left hand plenum (LHP) 20. In the LHP 20, hot HTF is distributed to the heat transfer inner flow core 8, and flows to the right in counterflow to the conveyed sand 15. The lower temperature sand is lifted out of the lower temperature in ground storage vessel 23 via a vertical conveyor 24 and enters the Archimedes screw sand conveyor 1 from a horizontal discharge auger 27 or other suitable conveyor. Heat transfer fluid 28 exchanges heat with conveyed sand 15 roughly in counterflow until it reaches right hand plenum (RHP) 21. HTF flows are combined in the RHP 21 and directed into the right hand large diameter pipe (RHLDP) 19, which is now used as the return pipeline. The conveyed sand 15 exits the Archimedes screw and enters storage vessel 22 view auger 26. Warm HTF in the RHLDP 19 returns to the outlet central large diameter pipe 17 and exits the Thermal Energy Storage system.

Embodiments of Discharging Processes to release stored thermal energy and heat the HTF are shown by a side view in FIG. 7. Again, this process will be largely similar regardless if practiced with in ground or above ground storage vessels. The operation of heating the HTF 28 is accomplished by using hot sand stored in the higher temperature in ground storage vessel 22. Warm HTF 28 flows in by way of an inlet large diameter supply pipe 16 and then flows in the right hand large diameter pipe (RHLDP) 19 into the right hand plenum (RHP) 21. In the RHP 21, warm HTF 28 is distributed to multiple pipes in the heat transfer tube bundle 8 and flows to the left in counterflow to the conveyed sand 15. The hot sand is conveyed 15 from the higher temperature in ground storage vessel 22 into the Archimedes screw conveyor 1 via vertical conveyor 24 and horizontal discharge auger 26 or other suitable conveyor and exchanges heat with the warm HTF roughly in counterflow. When the warm sand reaches the end of the Archimedes screw conveyor 1, it is returned to the lower temperature in ground storage vessel 23 where it awaits the Charging Process. The now hot HTF reaches the left hand plenum (LHP) 20 and is directed into the left hand large diameter pipe 18, now used as the return pipeline. Hot HTF then returns to the outlet large diameter supply pipe 17 and exits the Thermal Energy Storage system to produce usable energy.

Turning to FIG. 8, exemplary embodiments of storage vessels 102, 103 are illustrated in greater detail. The storage vessels 102, 103 may have angled walls 132 to facilitate flow of granular materials 15 into and out of the storage vessels during operation. In exemplary embodiments, the wall angle may be about 30° or greater. This advantageous configuration can be employed in either above ground or in-ground storage vessels.

In concentrator solar thermal power, embodiments of the disclosed systems and methods are used to store heat gathered during the day that is not needed for power generation or that is in excess of the heat needed for power generation at some time. This heat will be stored and used to generate power when needed, such as during afternoon peaking periods, or during the evening and nighttime. The basic concept of the sand shifter may be applicable in other applications in power generation cycles, in materials processing, or in other heating, cooling, and/or mass transfer applications.

It should be understood that good heat transfer performance is obtained by raining the sand 15 over a heat transfer tube bundle 8 carrying the HTF used to convey heat alternatively from the collector field or to a power conversion plant. Ideally, heat transfer coefficients moderately approximating the performance seen in similarly-agitated fluidized beds will be achieved. Good heat exchange effectiveness means close approach of the thermal storage medium to the inlet temperature of the HTF during charging of the storage and close approach of the HTF temperature to the maximum temperature of the storage medium during discharge. This good effectiveness will be obtained by heating sand or alternatively removing heat from the sand while moving the sand to or from a higher temperature above ground storage vessel 2 in a novel conveyor that doubles as a counter flow heat exchanger. The counter flow arrangement promotes high effectiveness. The sand storage containers will be simple and inexpensive insulated silos or bins above ground or buried pits.

Thus, it is seen that systems and methods of storing and releasing thermal energy are provided. It should be understood that any of the foregoing configurations and specialized components or chemical compounds may be interchangeably used with any of the systems of the preceding embodiments. Although illustrative embodiments of the present invention are described hereinabove, it will be evident to one skilled in the art that various changes and modifications may be made therein without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention. 

1. A system of thermal energy storage and release, comprising: at least one storage vessel; at least one heat transfer ramp adjacent to the at least one storage vessel; and at least one heat transfer fluid channel adjacent to the heat transfer ramp such that heat exchange occurs between a heat transfer medium traveling down the heat transfer ramp and a heat transfer fluid traveling through the heat transfer channel; wherein the heat transfer ramp is angled with respect to the storage vessel such that the heat transfer medium travels down the heat transfer ramp assisted by force of gravity.
 2. The system of claim 1 wherein the heat transfer medium is a granular material.
 3. The system of claim 1 wherein the at least one heat transfer ramp comprises at least two ramps in a substantially parallel layered configuration.
 4. The system of claim 3 wherein the at least one heat transfer fluid channel is disposed between the two ramps.
 5. The system of claim 1 wherein the at least one heat transfer ramp defines at least one slot.
 6. The system of claim 1 wherein the at least one heat transfer channel is coupled to one or more of: a side surface of the heat transfer ramp, a top surface of the heat transfer ramp, or a bottom surface of the heat transfer ramp.
 7. The system of claim 1 wherein the at least one heat transfer ramp comprises at least two ramps in a cascading configuration.
 8. The system of claim 1 wherein energy is stored as heat gathered by, or discharged to, a concentrating solar thermal power plant.
 9. A combined heat exchange and conveyance system, comprising: a bundled heat transfer assembly including at least two stacked heat transfer ramps and at least one heat transfer fluid channel adjacent to the at least two stacked heat transfer ramps; wherein a heat transfer medium is conveyed through the heat transfer ramps such that the heat transfer medium travels down the heat transfer ramps assisted by force of gravity and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs in the bundled heat transfer assembly between the heat transfer medium and the heat transfer fluid.
 10. The system of claim 9 wherein the heat transfer medium is a granular material.
 11. The system of claim 9 wherein the heat transfer ramps define at least one slot such that the heat transfer medium falls through the at least one slot in a first heat transfer ramp to a second heat transfer ramp below the first heat transfer ramp.
 12. The system of claim 9 wherein the at least one heat transfer fluid channel is disposed between the two stacked heat transfer ramps.
 13. The system of claim 9 wherein the at least one heat transfer channel is coupled to a bottom surface of one or more of the heat transfer ramps.
 14. The system of claim 9 wherein the at least one heat transfer channel is coupled to a side surface of one or more of the heat transfer ramps.
 15. A thermal heat transfer device, comprising: a combined heat exchanger and conveyor including at least one heat transfer ramp and at least one heat transfer fluid channel adjacent to the heat transfer ramp; wherein a granular material is conveyed through the at least one heat transfer ramp such that the granular material travels down the heat transfer ramp assisted by force of gravity and a heat transfer fluid is conveyed through the at least one heat transfer fluid channel such that heat exchange occurs between the granular material and the heat transfer fluid.
 16. The device of claim 15 wherein the granular material is sand.
 17. The device of claim 15 wherein the heat transfer channel is angled relative to the at least one heat transfer ramp.
 18. The device of claim 15 wherein the at least one heat transfer ramp comprises at least two ramps in a substantially parallel layered configuration and the at least one heat transfer fluid channel is disposed between the two ramps.
 19. The device of claim 15 wherein the ramps define at least one slot such that the heat transfer medium falls through the at least one slot in a first ramp to a second ramp below the first ramp.
 20. The device of claim 15 wherein the at least one heat transfer channel is coupled to one or more of: a bottom surface of one or more of the heat transfer ramps, a top surface of one or more of the heat transfer ramps, or a side surface of one more of the heat transfer ramps. 